Circuit breaker



1941. E. ORTENSI 2,250,599

C IRCUIT BREAKER Filed Feb. 15, 1940 2 Sheets-Sheet 1 WITNESSES: I INVENTOR Cay fizz/ uy. QWZ A July 29, 1941. E. ORTENSI 2,250,599

CIRCUIT BREAKER Filed Feb. 15, 1940 2 Sheets-Sheet 2 WITNESSES:

& y f77n/0 Orfenai.

I BY. f! r. Z

7 -Z/ATTORN Patented July 29, 1941 UNITED STATES PATENT OFFICE CIRCUIT BREAKER sylvania Application February 15, 1940, Serial No. 319,086

13 Claims.

This invention relates to circuit interrupters of the liquid immersed type and more particularly to improvements in operating mechanisms for securing the rapid separation of the interrupter contacts, a more positive circulation of arc extinguishing liquid within the arc extinguishing chambers, and an improved contact construction to insure positive engagement of the contacts in moving to the closed position.

In order to meet present day demands for high speed circuit breaker operation, designers have adopted spring means for accelerating the moving parts of the breaker mechanism and the movable contact structure. In the usual arrangement, the force of the accelerating spring is weakest at the end of the contact opening stroke which may permit the moving contact structure to rebound at the end of the opening stroke and thus interfere with the arc extinguishing function of the breaker.

In recent years, various schemes have also been devised, particularly in breakers of the liquid immersed type, for positively circulating arc extinguishing liquid within an arc rupturing chamber during the circuit interrupting operation. The means employed may constitute a piston associated with the arc chamber and which is adapted to be actuated simultaneously with the moving contact structure. It has been found that under certain conditions of operation the pressure within the arc chamber arising from the action of the are upon the liquid, is sufiicient to materially slow down the liquid moving means, and in some instances, stopping it entirely prior to the end of its stroke, thereby rendering the liquid circulating means ineffective. It is, of course, conceivable that the deleterious effect of the pressure within the arc chamber may be overcome by increasing the tension of the accelerating spring or springs.

This method of overcoming the difliculty merely introduces a further difiiculty which, from a commercial point of view, is perhaps more objectionable than the former, since for every increase in the accelerating force by means of springs, a corresponding increase in force is required to recharge the springs during the closing operation of the breaker. It has been found that the pressure created by the arc within the breaker casing may be utilized to assist the spring charged operating mechanism to ac celerate both contact separation and oil circulation. By utilizing the pressure generated by the arc in this manner, the tension of the accelerating spring may be materially decreased, thereby also reducing the force required for closing the breaker. It has also been found in connection with a contact construction which embodies a fixed contact which is spring biased into its closed position, that in closing the breaker an arc may be struck just prior to engagement of the contact which will develop sufiicient pressure to move the relatively fixed contact back against the bias of its spring to a position beyond the limit of travel of the movable contact so that the contacts never will completely engage. I propose to utilize the pressure developed by such an arc on closing the breaker contact, to aid the spring biasing the relatively fixed contact to maintain the contacts completely closed.

More directly stated, the objects of my invention are as follows: To improve the opening and closing performance of circuit interrupters of the liquid immersed type; to provide a contact structure for a circuit interrupter which is of the immersed type and embodies a spring biased relatively fixed contact with means for positively insuring engagement of the contacts in the closed position; to provide improved operating means for circuit interrupters of the liquid immersed type for securing a more rapid contact separation, a more positive circulation of arc extinguishing liquid within the arc chamber, and to obtain positive engagement of the contacts in the closed position thereof, by fluid operated or controlled means.

Another object of my invention is to provide an improved spring biased contact construction for circuit interrupters oi the liquid immersed type with means preventing separation of such a spring biased contact by an arc struck during the closing movements of a contact movably associated therewith.

Another object of my invention is to provide a simplified structural arrangement whereby the above-named objects may be effected in liquid immersed breakers employing a plurality of arc extinguishing devices connected in series.

Other objects and advantages relating to details of the structure will appear more fully upon consideration of the following detailed description of a preferred embodiment of my invention, taken in connection with the accompanying drawings, in which:

Figure 1 is a longitudinal sectional view showing a circuit interrupter embodying the improvements of my invention;

Fig. 2 is an enlarged longitudinal sectional view through one of the arc extinguishing units employed in the circuit interrupter of Fig. 1;

Fig. 3 is a fragmentary sectional view taken substantially along the line III-III of 1, and showing etails of the contact structure when the interrup is in the open circuit position; and

Fig. 4 is a cro sectional View taken substantially along the line IVIV of Fig. 1, showing the means for assisting the operating mechanism to actuate the interrupter to the open circuit position.

This invention is illustrated in conjunction with a circuit breaker of the type shown in the copending application of W. M. Leeds et 2.1., Serial No. 145,272, filed May 28, 1937, and allowed April 9, 1940 as Patent No. 2,196,419, which is assigned to the assignee of this application, and of which I am one of the joint invento s.

My invention is particularly adap ed for use in connection with circuit interrupters of the type shown and described in the applicedon, to which reference may be in the mode in which the instan be carried out.

Referring to Figure l of the rawings, tie reference 21 meral 5 designates a cylindrical casing havin an upper annular support plate 1, upon which is supported a cylindrical strain member 9 of insulating material, such as artificial resin impregnated fiber or the like. The lower end of the cylindrical strain member 9 is provided with a metallic flange Ii which serves as a convenient means for bolting the member 8 to the support plate '1'. The upper end of the cylindrical strain member 9 is provided with a metallic flange l3 to whic may be bolted an annular support plate l5. Surrounding the cylindrical strain member 9 is a cylindrical member I! of insulating and weatherproof og a ities, such as porcelain or the like. The weatherproof casing Il may be supported upon annular subcasing l9 secured to the support plate "I. A metallic flange member 2| secured to the lower edge of the weatherproof casing ll may be utilized in bolting the casing IT to the support l9 as shown.

Interposed between the support plate l5 and the top of weatherproof casing I! is a resilient expansion member preferably of metal, and having a C-shaped cross-section. The expansion member 23 compensates for any inequa ity of expansion between the strain member 9 and the weatherproof casing ll, thereby maintaining the latter in compression. It will, of course, be understood that gaskets may be inserted as shown between the joints of the various men rs above described for the purpose of preven the leakage of liquid wi h which the interrupter casing is filled.

The upper annular support plate 5 is provided with a hanger plate 25 from which is suspended a plurality of, in this instance two, are extinguishing units 2?. The arc extinguishing units 21 are similar to those shown and described in the aforenamed application and are adapted to be assembled upon four tie rods 29, only one of which is shown. The upper ends of the rods 23 have a threaded portion passing through the hanger plate 25 for the reception of nuts 3!. In order to maintain the individual ing units 2'! in proper spaced relation spect to each other and to the Lange adjustable spacing sleeves 33 are provided rounding the hanger rods 29.

Each of the arc extinguishing units, as more clearly shown in Fi 2, comprises a plurality of plates of insulating material disposed between an upper end plate 35, preferably of metal, and a lower end plate 37, preferably of insulating material. The intermediate plates designated as at 39, 4|, 43, 45, 4'! and 49 each have a slotlike aperture therethrough to provide a relatively narrow arc chamber generally designated at 5!. These latter plates are preferably of insulating material, such as fiber, and are also provided with a circular aperture joining one side of the slot-like apertures to provide a cylindri al passage 53, the purpose of which will appear more fully hereinafter. The plates are provided with U-shaped inserts of magnetic material 55 disposed with their parallel elements on opposite sides of the slot-like passage 5! so as to provide means for moving an arc laterally within the passage.

The upper end plate 35 carries a movable contact carrying member 51, which is resiliently mounted. The contact carrying member 57 has a stationary contact 6! secured thereto, which contact is adapted to extend through the end plate 5 into the arc passage 5!. The outer portion of the contact carrying member 51 extends through a cylindrical housing 55 which, as shown, has an open end thereof secured to the upper end plate 35 as by welding or the like, and has an end cap 58 threadedly mounted on the outer end t1 ereof. The end cap 58 is provided with a central aperture through which the outer end of the contact carrying member 5'! extends to be connected to the flexible conductor 10! as by the nuts 59 threadedly engaging the outer end of member 57. Within the cylinder 56, the contact carrying member 5! is provided with an integral disc-like portion G0 which closely fits within the cylinder 56 in a piston-like manner. The spring 54 for resiliently biasing the contact Bl in a direction into the arc passage is held under compression between the disc-like piston member 60 and the cap 58 for the outer end of the cylinder 56. The movable contact member 51 and the contact portion 61 are provided with a longitudinally extending bore or passage 62 extending centrally from the free end of the contact 6| to a point above the piston member 80 where it communicates with a cross passage 64 extending through the contact carrying member 5'! so as to connect the free end of the contact Bl with the space in the cylinder 58 above the contact piston 69, all for a purpose to be hereinafter described. The stationary contact BI is adapted to be engaged by a moving contact 63, which is carried by the contact support member 65. The moving contact 63 is provided with depressed or cutout portion 65 which is adapted to substantially register with and is slightly larger than the end of the passage 62 in the contact 6| to prevent blocking of the passageway 62 when the contacts are moved into engagement.

The support member 65 is provided with the tubular metallic coupling member 61 secured to the lower end thereof. The tubular coupling member 6! is provided with an upstanding rod 69 of insulating material having a metallic coupling ll secured to the upper free end thereof. The rod 52 is adapted to support a piston 13 which is maintained in assembled position upon the rod 69 by means of nuts screw threaded onto the metallic portion H.

The metallic coupling member 6'! of the upper unit 21 is adapted to be joined to the metallic coupling member ll of the next lower unit 21, and by a flexible shunt I23 to the next lower contact member 51, thereby connecting the two units electrically in series and at the same time coupling the contact carrying members 65 and the pistons 73 in tandem for simultaneous actuation.

The coupling member 61 of the lower unit 21 is provided with yieldingly mounted contact fingers l'l adapted to engage a contact actuating member 19, which contact actuating member is adapted to be actuated vertically in straight line motion by an actuating linkage generally designated at 8|. The lower end of contact actuating member 19 is provided with a guide member 83 which is adapted to be slidably received by a guide tube 85 extending through and secured to the base of the casing 5.

The metallic coupling H of the arc extinguishing unit 21 is provided with a coaxially aligned operating rod 37, which rod extends upwardly through a cylindrical casing 89. The cylindrical casing 89 is supported and secured to a plate 9| having a flange 93 which in turn rests upon the upper annular plate I5. The upper end of the operating rod 87 terminates in a spring chamber 95 and is provided with a guide member 97. Interposed between the guide member 91 and the removable top plate 99 of the spring chamber 95 is an accelerating spring NH.

The moving contact assemblage, in accordance with the foregoing description, comprises the guide member 9?, operating rod 81, metallic coupling member H of the upper unit 21, the insulating rod 59 carrying the contact support 55 and the movable contact 63, the metallic coupling member 61, which is joined to the metallic coupling member ll of the lower unit 21, which unit also has an insulating rod 59, contact carrying member 55 of the lower unit and its movable contact 63, the lower metallic coupling member 61 carrying contact fingers 1'! in turn engaging the movable contact actuating member 19. This assemblage also carries the pistons 13 disposed about the insulating rods 69. Thus actuation of the operating linkage 8| will operate the movable contact assembly as a unitary structure to open and closed positions. During movement of the assemblage upwardly to the closed circuit position, the linkage 8| is required to overcome the bias of the accelerating spring [L When in the closed circuit position, as shown in Fig. 1, the electrical circuit through the interrupter proceeds from the line terminal I03 through the flexible connection I05, connection 501 to the contact carrying member 51 of the upper unit 21, contact 6|, movable contact 63, contact carrying member 65, coupling member 61, shunt l23, Contact member 51 of the lower unit 21, from whence the circuit proceeds through the lower unit 27 in like manner as the upper unit and emerges at the contact fingers I! and proceeds to the contact actuating member 19. The contact actuating member 19 is provided with a flexible conductor I09, which is joined with a conductor connected to the base of the easing which may serve as the other line terminal of the interrupter.

Upon operating the interrupter to the open circuit position, the actuating mechanism of the interrupter (not shown) through the medium of an actuating rod H3 operates the linkage 8| which in turn lowers the contact actuating member 19, thereby permitting the accelerating spring lill to move the operating rod 81 and the entire movable contact assemblage of both are extinguishing units 21 to the open circuit position. The are established between the stationary contact El and the movable contact 63 of each unit will be moved laterally in the arc passage 5| onto the arc horns H5 and H1 disposed in the upper and lower ends of the arc passage.

The products of decomposition of the are are permitted to escape from the passage 5| through a vent opening H9 provided in the plates 35 and 39 of each arc extinguishing unit 21 which join the rearward end of the slots in the respective plates forming the passage 5|. Thus the pressure developed in each of the arc extinguishing units 2'! resulting from the formation of the are therein is communicated to the liquid contained within the enclosure defined by the cylindrical strain member 9.

When the arc has been moved onto the upper and lower arc horns H5 and Ill, respectively, the electrical circuit through the two are extinguishing units proceeds from the upper contact carrying member 5! of the upper unit 2'! to the metallic end plate 35, the upper arc horn H5 through the arc to the lower arc horn H'l, connection |2| to the upper plate 35 of the lower unit 21, through which it proceeds in a similar manner as for the upper unit 21, and emerges at connection I23 which is in turn connected to the contact fingers 11.

During the opening movement of the movable contact 53, the action of piston 13 in the cylindrical passage 53 circulates arc extinguishing liquid contained within the passage into engagement with the are, thereby forcing the products of decomposition of the are from the arc passage substantially as rapidly as they are formed. The arc passage 5|, as more specifically disclosed in the aforenamed application, has a configuration such that movement of the arc laterally toward the rearward portion of the passage 5| does not take place until the arc has a predetermined cross-sectional area. In other words, the arc is permitted to play in an enlarged portion of the passage in the region of the contacts 6| and 63 until its cross-sectional area has been reduced sufliciently to permit entrance into the restricted portion Just prior to the current zero, whereupon it may readily be moved by the magnetic action of the U-shaped plates 55 into the constricted portion rearwardly of the passage 5|. While in this constricted portion, the arc is subjected to a turbulent cross blast of the products of decomposition of the arc and also to the flow of oil resulting from the action of the piston 13. The turbulent intermixing of un ionized gas and oil particles with the arc while being thus confined subjects the arc stream to a rapid deionizing action, so that when the arc current passes through its zero value in the current wave, the conductivity of the arc path has been decreased to such an extent that the arc will not restrike when the voltage builds up in the opposite direction. In operating the movable contact assemblage to the fully open position, the moving contacts 63 are brought to rest against the lower end plates 31 of each arc extinguishing unit 2?. The contact actuating member 19, however, is free to continue its downward movement for a predetermined distance, causing the contact fingers H to be disengaged therefrom to thereby introduce an additional gap in the circuit, as shown in Fig. 3.

It will be noted that the formation of the arc in the passage 5| of each unit 21 may produce considerable pressure, which would ordinarily react on the lower exposed face of the support member 65 of the piston 13, thereby tending to retard the opening movement of the contacts 63. In order to overcome the retardation of the moving contacts 63 during the opening operation and also to increase the speed of separation of the contacts even though a relatively low tension accelerating spring IElI is used, there is provided an accelerating device that utilizes the pressure communicated from each unit 21 to the enclosure defined by the cylindrical strain mem ber 9.

The upper end of the strain member 9 is substantially enclosed by the support plate SI and the cylindrical n ember 89. Within the cylindrical chamber 89 is provided a movable piston or baffle member I25 which in turn is carried by a tubular member I21 extending therethrough in coaxial alignment therewith. The tubular member I21 has an enlarged annular cross-sectional or piston portion I29 extending above the bailie 25, and is adapted for sliding movement in an inner cylindrical casing I3I. The upper ends of the coaxially disposed cylindrical casings 89 and NH are respectively enclosed by the plate 90 supporting the spring housing 95. The operating rod 81 is provided with a piston I33 rigidly secured thereto and slidably operative in the bore of the tubular piston I29. The baffle member I25 and its cooperating tubular piston member I29 are biased downwardly by a spring I35 encircling the inner casing I3I, so that the lower end of the tubular member I21 normally rests upon the hanger plate 25.

The side walls of the cylindrical casing 89 are provided with a series of graded vent openings or apertures as indicated at I31. These vent openings are positioned adjacent and immediately above the baffle member I25 when the baffle is in its normal position, as shown in Fig. l, and have successively increasing areas in the upward direction. The inner cylindrical casing I3I is also provided with a series of apertures or vent openings, in this instance preferably in the form of segmental circumferential slots, and shown at I39. The vent openings I39 are positioned just above the upper edge of the tubular piston I29 when the piston is in its normal po sition as shown.

A cylindrical casing I4!) is preferably sealed at its lower end to the annular support plate I5 and extends upwardly beyond the cylindrical chambers 89 and I3I so that these chambers may be completely submerged in arc extinguishing liquid. A hood I42 bolted to a flange I44 of the casing I48 encloses the upper end of the circuit interrupter housing.

From the foregoing description, it follows that as the operating rod 81 is moved downwardly during the circuit opening operation carrying with it piston I33, liquid will be drawn in through the apertures I39 to maintain the inner casing I 3| filled with liquid. As soon as the pressure resulting from the arcs within the interrupting units 21 builds up within the tubular strain member 9, this pressure will react upon the baffle member I25, which is free to move vertically within the outer cylindrical casing 89, to thereby actuate the tubular piston I29 upwardly, which seals the apertures I39 and subjects the liquid within the inner cylindrical casing I3I to pressure, which pressure reacts downwardly upon the piston I33 to assist the operating rod 81 to move the contacts 63 to the open position and to force the piston 13 against the pressure set up within the arc passages 5I. Movement of the baffle member I25 upwardly also uncovers the vent openings I31 through the side walls of the cylindrical chamber 99 to thereby relieve the pressure within the casing 9.

As soon as the pressure subsides within the casing 9 following the interruption of the circuit, biasing spring I35 assisted by gravity again returns the baflie member I25 and its associated tubular piston I29 to the normal position. In this position, the ports or vents I39 are again uncovered, and operating rod 81 with its piston I33 are free to be moved vertically in order to return the interrupter to the closed circuit position. It will thus be seen that the movable contacts with their associated pistons 13 are free to be moved to the open and closed circuit position independently of the baffle member I25.

With the above arrangement there may be conditions under which the pressure within the casing 9 is insufficient to cause upward movement of the baffle member I25 until the operating rod 81 and the contacts 63 have reached their full open position. The delayed upward movement of the bafile I25 under these circumstances immediately seals the ports I39 prior to uncovering of the ports I31. Therefore, unless further provision is made to relieve the pressure within the inner cylindrical casing I3I, further upward movement of the bailie I25 is prevented which may result in building up pressure within the casing 9 to a dangerously high value. In order to relieve the pressure within the cylindrical casing I3I at the end of the opening stroke, we have provided vents or notches MI in the operating rod 81 adjacent the guide member 91. These notches permit the relief of pressure from within the casing I3I to the spring chamber 95 and into the casing by way of the vent I45. Thus a relief of pressure in the inner chamber I3I permits the baffle I25 to be raised and relieve the pressure within the casing 9 through the ports I31.

It may also occur that during the closing operation of the interrupter during conditions of load that an arc may be established between the contacts prior to the complete closing of these contacts which may build up suflicient pressure within the casing 9 to raise the bafile I25, thereby sealing off the openings I39 and stall the piston I33 and its operating rod 81, thereby preventing the completion of the closing stroke. Thus an arc may be maintained for a period of time sufficient to cause a pressure within the casing 9 high enough to injure the interrupter casing. In order to avoid this injurious effect, we have provided a second series of openings or notches on the operating rod 81 located as indicated at I43. The notches I43 are so positioned with respect to the upper wall of the inner casing I3I that the pressure Within the latter casing is relieved just before the contacts GI and 53 make engagement with each other. The notches I43 are, however, so arranged that upon final movement of the contacts 63 to the fully closed position, the enclosure within the casing I3I is again sealed, thereby preventing further movement of the bafile in the upward direction which might put it in the uppermost position of its path of travel and render it useless in the event that it were called upon to operate in an immediate interrupting operation following the closing of the breaker contacts.

It has been found that when an arc is established between the contacts prior to the complete closing of these contacts, if sufficient pressure is not built up to raise the baffle I25, or, in any event there may be sufficient local pressure, especially as the moving contact 63 closely approaches the closed position, to raise the contact 6| against the force exerted by its biasing spring 54 to a position beyond the range of upward movement of the contact 63 so that the arcing will persist and the contacts may never completely close. Even where sufiicient pressure is generated by an arc struck during the closing movement of the contact to raise the baffle I25 in the manner described above, suflicient pressure may be immediately developed to cause the contact 6| to recede and even though the pressure is relieved through the notches N3 of the operating rod 81 up to immediately before the contacts engage, the contact 6| will nevertheless be maintained in a raised position due to the pressure of the are being confined between the closely spaced contacts to maintain the contact 6| in an open position for a considerable period of time. Such an operation, of course, has a deleterious effect on the contacts themselves, as Well as being another source of objectionable pressure within the interrupter casing.

Obviously, with the contact structure described and shown herein, when the movable contact 63 is moved toward its closed position relative to the contact 6|, any pressure that may be built up by an arc striking before the contacts are closed will be immediately transmitted by way of the contact passages 62 and 64 to the upper side of the contact piston 60, thereby opposing the pressure exerted on the lower end of the contact El and allowing the spring 54 to maintain the contact 6| in a position in which it may be positively engaged by the moving contact 63. As is obvious from: an inspection of Fig. 2, the upper side of the contact piston 60 has a larger exposed area than the free end of the contact 6| and therefore, the pressure transmitted from between the closing contacts 63 and GI to the upper side of the contact piston 60 will be distributed over a greater area in tending to move the contact in the downward direction, than the pressure tending to move the contact in an upward direction. Therefore, the pressure developed by an arc struck between the contacts when closing actually is multiplied and added to the pressure of contact spring 54 to maintain the contact 6| in a position in which it will be positively engaged by the moving contact 63 to thus insure a positive engagement of the contacts in the closed position of the breaker.

From the foregoing description, it follows that the movable interrupter contact may be moved to the open position irrespective of the pressure conditions within the casing and also may be moved to a closed position with positive contact engagement being obtainable irrespective of the pressure conditions within the casing 9.

It should be obvious that in accomplishing the above results, I have provided a structure so constructed and arranged as to embody fluid operating means, or a structure wherein fluid is permitted to directly effect these operations.

Having described a preferred embodiment of my invention in accordance with the patent statutes, I wish it to be understood that I do not wish to be limited to the particular embodiment disclosed herein, inasmuch as it will be obvious, particularly to persons skilled in the art, that many changes and modifications may be made in this particular structure without departing from the broad spirit and scope of my invention. Thus, for example, my improved contact construction would be readily applicable to a circuit breaker construction such as that shown in the patent to W. M. Leeds et al. No. 2,138,382, issued November 29, 1938, of which I am a joint inventor, and which patent is assigned to the assignee of this application. Therefore, I desire that my invention be interpreted as broadly as possible and that it be limited only by what is specifically set forth in the following claims.

I claim as my invention:

1. In a circuit interrupter, an arc casing having a resiliently biased contact extending through a wall of said casing, movable contact means movable into and out of engagement with said contact to draw an arc in said casing, and a vent passage through said contact extending from the contacting portion of said contact to the outside of said casing, and constructed at the end thereof at said contacting portion so as not to be blocked by engagement of said movable contact means therewith.

2. In a circuit interrupter, an arc casing having a contact extending through a wall of said casing and resiliently biased inwardly, movable contact means movable into and out of engagement with said contact to draw an arc in said casing, and means for transferring any pressure exerted on the portion of said contact within said casing to a portion of said contact outside of said casing and in an opposite direction.

3. In a circuit interrupter, an arc casing having a contact extending through a wall of said casing and resiliently biased inwardly, movable contact means movable into and out of engagement with said contact to draw an arc in said casing, and hydraulic, force-multiplying-means for transferring any pressure exerted on the portion of said contact within said casing to a portion of said contact outside of said casing and in an opposite direction.

4. In a circuit interrupter, an arc casing, a resiliently biased contact, movable contact means movable into and out of engagement with said contact to draw an arc in said casing, hydraulic force-multiplying-means for transferring any pressure exerted on the portion of said contact within said casing to a portion of said contact outside of said casing and in an opposite direction, and said contact being biased in a direction toward said contact means in the closed position of said contact and contact means.

5. In a circuit interrupter, an arc casing, a resiliently biased contact, movable contact means movable into and out of engagement with said contact to draw an arc in said casing, means for transferring any pressure in said casing, tending to separate said contact and contact means when they are in a closed position to said contact and in a reverse direction to neutralize the same and permit said resilient bias to maintain said contact and contact means in engagement.

6. In a circuit interrupter, an arc casing having an apertured wall, a contact member in said aperture and resiliently biased inwardly, a cylinder compartment about an outer portion of said contact member, piston means on said contact member, and said cylinder communicating outwardly of said piston means with the space adjacent the contacting portion of said contact member.

7. In a circuit interrupter, an arc casing having an apertured wall, a contact member extending through said aperture and resiliently biased inwardly, a cylinder compartment about an outer portion of said contact member, piston means fixed on said contact member, and said cylinder communicating outwardly of said piston means with the space adjacent the contacting portion of said contact member, and the eliective area of said piston means being greater than the effective area of said contact portion.

8. In a circuit interrupter, an arc casing having an apertured wall, a contact member in said aperture and resiliently biased inwardly, a cylinder compartment about an outer portion of said contact member, piston means fixed on said contact member and forming a substantially fluid tight partition in said compartment, said contact member including a passage connecting the outer end of said cylinder compartment with the contacting portion of said contact member.

9. In a circuit inte 'rupter, an arc casing having an apertured wall, a contact member extending through said aperture and resiliently biased inwardly, a cylinder compartment about an outer portion of said contact member, piston means fixed to said contact member, and said cylinder communicating outwardly of said piston means with the space adjacent the contacting portion of said contact member, and the portion of said cylinder compartment inwardly of said piston means communicating with th atm sphere outside of said casing.

10. In a circuit interrupter, an arc casing having an apertured wall, a contact member in said aperture and resiliently biased inwardly, a cylinder compartment about an outer portion of said contact member, piston means integral with said contact member, and said cylinder communicating outwardly of said piston means with the space adjacent the contacting portion of said contact member, and a second contact member mounted for movement into and out of engagement with respect to said first contact member.

11. In a circuit interrupter, an arc casing having an apertured wall, a contact member in said aperture and resiliently biased inwardly, a cylinder compartment about an outer portion of said contact member, piston means fixed to said contact member, and said cylinder communicating outwardly of said piston means with the space adjacent the contacting portion of said contact member, and a second contact member mounted for movement into and out of engagement with respect to said first contact member, said second contact member being configurated in a manner to prevent blocking of said communication.

12. In a circuit interrupter, a casing containing arc extinguishing liquid, separable contacts within said liquid at least one of which is springbiased toward the other of said contacts, means for operating said other contact to open and closed positions with respect to said one contact,

eans responsive to the pressure within said casing for aiding the opening movement of said other contact, and for aiding said spring bias to maintain said contacts engaged in the closed circuit position.

13. In a circuit interrupter, an arc casing having a resiliently biased contact extending through a wall of said casing, movable contact means movable into and out of engagement with said contact to draw an arc in said casing, and vent means extending from the contacting portions of said contact and contact means to the outside of said casing, and said contact and contact means arranged so as not to block said vent means when they are in engagement.

ENN'IO ORTENSI. 

